Duke U. discovers new use for laser in art world

DURHAM, N.C. (AP) — A Duke University professor who developed a laser to study melanoma has discovered a new use for the system: uncovering what's underneath artwork without damaging the pieces in any way.

Dr. Warren S. Warren was at the National Gallery in London, looking at an exhibit on art forgeries, when he realized that the art world used imaging technologies that were 30 or 40 years old. So he began investigating whether lasers could be used to uncover the mysteries underneath layers of paint without damaging the art.

So far, the answer is a qualified yes.

Warren and others in Duke's Center for Molecular and Biomedical Imaging, which he heads, have discovered they can use Warren's pump-probe laser to create three-dimensional cross-sections of art that let researchers see colors and layers and maybe, at some point, discover the source of materials.

"It's not ready for prime-time, but it's showing some real promise, and that's exciting," said John Delaney, senior imaging scientist in the conservation division of the National Gallery of Art in Washington, D.C. Delaney, who researches how to adapt noninvasive analytical imaging methods to help identify and map artists' materials, has traveled to Durham to see the laser system at work.

The first beneficiary of the laser is the N.C. Museum of Art, about 60 miles southeast of Durham. The museum and the school are figuring out together how to make the pump-probe laser work optimally for art conservationists.

The museum's 14th-century "Crucifixion" by Puccio Capanna was the first painting to get a pump-probe laser exam. It revealed a thick layer of lapis lazuli over Madonna's mantle, said William Brown, the museum's chief conservator. Typically, that blue is achieved with a layer of the less expensive azurite, covered with a thin layer of lapis, which was more expensive than gold at the time, he said.

"This tells us it was a really important painting," said Brown, adding that it could be part of an altarpiece at the Vatican.

The museum is contributing about $12,500 a year in grant funds to research its paintings, while the school received a three-year grant of about $700,000 from the National Science Foundation to investigate the laser's use for both cancer and art research. Warren's lab will use part of the NSF grant to develop a portable version of the pump-probe so it can go to the paintings, rather than the other way around, and so it can be used to examine larger works of art.

The research matters well beyond telling visitors that another face lies under the one they see now or that the red glaze and lapis paint were mixed, rather than layered, Brown said.

"Through these techniques, you're also understanding the technology that went into the creation of these paintings," Brown said. "And you can chart the whole history of the world through technology and technology innovations. It affects the economy, it affects everything."

Typically, an art conservationist uses a scalpel to remove tiny samples from a painting to learn more about both the painting itself and the materials used. That method damages the painting and also is limited in where a conservationist can nick at the paint — corners and background, for example, and but not faces.

The pump-probe laser system provides a three-dimensional view of any part of a painting without taking a chip. Researchers can zoom in and out, like looking at a layer cake, and separate colors to see what was originally on the canvas.

Warren explained that the pump-probe laser uses two laser pulses of different colors and varies the delay between the pulses. The first one "pumps" the pigment and the second one "probes" what happened to the energy deposited by the first one.

Other science applications need two well-synchronized lasers, and they also could be used to examine paintings, Warren said. It could have happened a decade ago, but apparently no one thought to do it until he wandered into London's National Gallery.

The scientists are adjusting the laser wavelengths and looking for more colors than are needed for medical work.

"Biological samples are less complicated than paintings, and we didn't need to be flexible," Villafana said. "We had the system set up for the melanoma we were studying, and we didn't really need to change wavelengths anymore. Now we've got God knows how many pigments sitting in a mixture or a layer, and you need to see all of them."

So far, she's seen red, blue, yellow, brown and one green. The laser is tuned to the edge of green but "all we would need to do is rearrange some of the optics in there and we could make it put out green light or any color that we want," Warren said.

Art conservationists also push the scientists, Villafana said.

"Sometimes you want to see if there are previous restorations. Sometimes you want to say, what's the binder they used here? What thickness was this layer? It's about coming up with new and different ways to investigate a different problem."

While the laser system isn't yet optimal, it is attracting attention from other conservationists, including those who care for the Dead Sea Scrolls, Warren said. They want to know if the pump-probe can let them read what's in scrolls that are too fragile to unwind. And Brown hopes the laser one day will provide evidence that the Puccio was part of the Vatican altarpiece, perhaps by proving the lapis has the same chemical composition.

"It's not going to replace other tools, but it gives us different information," he said.

And it doesn't have to do everything, said Delaney, of the National Gallery in Washington. "Nothing has to be perfect," he said. "We're looking for what can help us solve problems that we don't have a good way to solve now. And this shows some potential."